The present invention relates to a pneumatic tire, more particularly to a structure of buttress which can be incorporated in a winter tire as well as summer tire to improve snow performance, especially lateral grip performance without sacrificing other performances.
Heretofore, in order to improve snow performance, block type tread patterns made up of siped blocks are usually employed and the percentage of the grooved area of the pattern is increased.
In such measures, however, with increase in the percentage of the grooved area, the pattern rigidity is decreased, and there is a tendency that the steering stability during running on dry roads is deteriorated. Further, as the groove volume is increased, there is a tendency that the following noise sound increases: a pitch sound generated when the groove edges contact with the ground; a pumping sound generated when air compressed in a groove jets out; and a resonance sound generated when air in a wide circumferential groove is resonated.
Canada Patent Application Publication No. 2006573 discloses a pneumatic tire which can be improved in snow performance without sacrificing other performances. As shown in FIG. 7, this tire is provided in the buttress parts (a) with rib-like protrusions (c). In order to improve the traction during running on snowy roads, the rib-like protrusion is provided on both sides in the tire circumferential direction with wall surfaces (CS) protruding from the surface of the buttress part (a). The rib-like protrusion (c) has a top surface (c) which merges into the surface of the buttress part (a). Such rib-like protrusions can not improve lateral grip on snowy roads in order to prevent side skid.